import threading
import time


def excutor(*args):
    print('this is my website www.google.com/%s' % i)
    time.sleep(2)
    args[0].release()


# limit of maximum of threads
sem = threading.Semaphore(value=3)
for i in range(20):
    sem.acquire()
    t = threading.Thread(target=excutor, args=(sem,))
    t.start()
